Cellular immunity, especially cytotoxic T cells (hereinafter referred to as CTLs), play an important role in eliminating tumor cells, virally infected cells, etc., from the living body. CTLs recognize a complex of an antigenic peptide (tumor antigen peptide) on a tumor cell and an MHC (Major Histocompatibility Complex) class I antigen, which is referred to as HLA antigen in the case of humans, and attack and kill the tumor cells.
Tumor antigen peptides are generated by intracellular degradation of proteins specific for tumors (i.e., tumor antigen proteins) by proteases, after the proteins are synthesized in cells. The resulting tumor-antigen peptide binds to an MHC class I antigen (HLA antigen) in the endoplasmic reticulum to form a complex, which is transported to the cell surface and presented as an antigen. The tumor-specific CTLs, when these recognize the complex presented as an antigen, exhibit anti-tumor effects through the cytotoxic actions or production of lymphokines. The elucidation of a series of these actions has allowed therapies which boost tumor-specific CTLs in patients with tumors by using tumor antigen proteins or peptides as so-called cancer immunotherapeutic agents (cancer vaccines).
Tumor antigen proteins include, as representative examples, ones listed in Table 1 of Non-Patent Document 1. Further, a papillomavirus binding factor (PBF) which recognizes the E2 binding site of papillomaviruses (GenBank Database Accession No. AF263928, SEQ ID NO:2) was reported as a tumor antigen protein applicable to cancers (tumors) including sarcomas (e.g., osteosarcoma) (patent document 1). In addition, tumor antigen peptides binding to the HLA-A24 or HLA-B55 antigen were identified. However, PBF-derived tumor-antigen peptides which bind to an HLA-A2 antigen have not been found yet.    [Non-Patent Document 1] Immunity, vol. 10:281, 1999    [Patent Document 1] International Publication No. WO 04/029248
These documents are incorporated herein by reference.